As the population is getting older nowadays, the number of people with mastication and swallowing disorders who have impaired chewing and swallowing abilities is increasing. When accidental aspiration of a water-containing food occurs in a person with mastication and swallowing disorders, the food enters the bronchi and may cause a severe disease such as pneumonia. Therefore, it is necessary to pay special attention to ingestion of low-viscosity foods such as tea, milk, juice, and soup.
For the people with mastication and swallowing disorders, many products of thickening compositions for increasing the viscosity of liquid foods, which are so called thickening agents or swallowing aids, have been developed and put on the market. Especially, thickening compositions have been recently required to not only be resistant to the formation of unmixed lumps (“DAMA” in Japanese) or large unmixed lumps (“MAMAKO” in Japanese) when dissolved in water-containing foods, but also have characteristics such as rapid dispersing and expression of viscosity, good flavor and taste, high transparency, and low production costs.
Patent Literatures 1, 2, and 3 disclose a thickening composition having an improved viscosity expression property and a method in which an aqueous metal salt solution is sprayed onto the surface of a xanthan gum powder followed by granulation. Meanwhile, Patent Literature 4 discloses a method in which fluidized-bed granulation of xanthan gum or the like is conducted by using an aqueous solution containing calcium pantothenate as a binder. Further, Patent Literature 5 describes the use of an aqueous solution containing ascorbic acid or its related compound as a binder. In these methods, presumably, the surface of xanthan gum or the like is coated with the metal salt or the ascorbic acid or its related compound, so that the wettability of the surface with water is improved, and the water-dispersibility is improved. However, in each of these methods, it is necessary to directly spray-coat the surface of xanthan gum or the like by using an aqueous solution of the metal salt, ascorbic acid, or the like. Hence, these methods have such problems that the addition of a predetermined amount of the metal salt or the like by spraying to obtain the effect is not simple, and that it may be difficult to control the particle size depending on the type and amount of the metal salt or the like dissolved in the spraying liquid and on factors such as the amount of the liquid sprayed. In addition, since the metal salt or the ascorbic acid or its related compound is directly attached as a coating to the surface of xanthan gum or the like, there is a concern about an influence on the quality of tastes, such as the saltiness, the bitterness, and the sourness, when certain types of metal salts or the ascorbic acid or its related compound are used.
In addition, Non Patent Literature 1 describes two-step granulation for obtaining a uniform thickening agent. In this two-step granulation, granules of a thickening polysaccharide alone are produced in primary granulation, and then granules as a finished product are produced in secondary granulation by again granulating the granules obtained in the primary granulation together with a dispersant such as dextrin. In principle, granulation is a process which requires high costs and long time. Hence, the granulation conducted two times in separate two steps presents a big problem in terms of costs, even though a good product can be obtained.
Patent Literature 6 discloses a thickening composition having an improved dispersibility, which comprises a metal salt-containing starch degradation product and a thickening polysaccharide. Patent Literature 6 also discloses that, in the thickening composition, the content of the metal salt is preferably 0.5 to 40 parts by mass relative to 100 parts by mass of the starch degradation product, and the mass ratio of the starch degradation product containing the metal salt to the thickening polysaccharide is preferably from 55:45 to 99:1.
However, the ratio of the starch degradation product to the thickening polysaccharide is relatively high in this composition, and the amount of the thickener required to be added to a target food to obtain the thickening effect is two times or more the amount in the case where the thickening polysaccharide is used alone. Accordingly, the possibility that this composition may affect the physical properties, the texture, or the taste of the food is undeniable.